Mobile communications that use public networks typified by cellular phones have widely prevailed for their conveniences. In public networks, a terminal can wirelessly connect to a base station to use various network services suck as the Internet via networks of providers. Moreover, services based on connections among terminals, such as telephone calls, file exchanges, and games, can also be used.
Since the public network and terminals are connected wirelessly (communication using such a connections will be referred to as “network communication”), a capacity of a wireless segment becomes insufficient due to an increase in the number of terminals connected to the public network to lower a service quality (e.g., unable to connect, communication speed is lowered, etc.), which is a problem. Further, since data of many terminals needs to be processed, problems of capacity shortages and line congestions arise also in the base station and core networks.
In a public network system, even services based on connections among proximate terminals use communications via the base station and core networks.
On the other hand, in recent years, in addition to a wireless system of connecting to public networks, other wireless systems (e.g., wireless LAN) that enable a direct communication between proximate terminals are being adopted in terminals (direct communication between terminals using this wireless system will be referred to as “direct communication”).
For example, Patent Document 1 discloses a melted of switching from a communication that uses a public network to a direct communication. The method of determining a terminal to perform a direct communication involves estimating a distance between terminals based on positional information of the terminals estimated by a base station and estimating an electrical field intensity of the terminals when the direct communication is performed based on the estimated distance, to judge whether the direct communication is possible.
Patent Document 1: Japanese Patent Application Laid-open No. 2001-238264